Fouqué befriended Crown Prince Frederick of Prussia, visiting him while the crown prince restricted to Küstrin.[1] Fouqué was a common guest of Frederick's at Rheinsberg. Frederick nicknamed his friend 'Chastity', and Fouqué was allegedly one of the best actors at the Prussian court.[2] Amongst his closest friends, Frederick formed the "Bayard Order" to study warfare. Fouqué was the grand master of the gatherings, at which archaic French was used.[3]

After a dispute with Leopold over his lack of promotion, Fouqué left Prussia to enter Danish service. When Frederick acceded to the throne in 1740, he induced Fouqué's return by promoting him to Oberst on 26 July, making him commander of the newly created Füsilier-Regiments Nr. 37, and awarding him the Order of the Black Eagle.[4]

In 1757 during the Seven Years' War, Fouqué hanged the Catholic priest Andreas Faulhaber for allegedly inciting Glatz's garrison to desert.[6] Frederick entrusted Fouqué with 13,000 troops in order to guard Silesia against enemy attacks.[7] In June 1760, the outnumbered Fouqué was forced to withdraw from combat by an Austrian force three times as large led by Ernst Gideon von Laudon.[8] When Frederick ordered the general to advance again, 8,000 troops under Fouqué were defeated in the resulting Battle of Landeshut on July 23. Wounded thrice by sabres, Fouqué would have died if not for his hostler, Trautschke, who alerted the Austrian dragoons they were attacking a commanding officer. When the dragoon leader Colonel Voit protected Fouqué and offered him his horse, Fouqué replied, "I might soil the fine saddle with my blood," to which Voit responded, "My saddle can only gain from being stained by the blood of a hero." When Frederick heard about Fouqué's capture and behavior, he stated, "Fouqué behaved like a Roman."[9]

Fouqué was released from Austrian captivity in 1763 when the war ended. Needing to use a wheelchair and believing himself dishonored by the defeat at Landeshut, Fouqué refused Frederick's offer to return to Glatz and instead retired to Brandenburg an der Havel. The king in Potsdam and the general in Brandenburg frequently corresponded with each other through gifts of food and drink.[10] After Fouqué died in Brandenburg, his biography was written by his grandson, Friedrich de la Motte Fouqué.